Lawn mower height-adjust systems are basically of two types: those in which individual adjustments are made to each wheel height, and those in which the positions of two or more wheels are adjusted simultaneously. Both types of height-adjust systems are found predominately in use with metal lawn mower decks. Very few address the problems associated with mounting a height-adjust system onto a plastic deck and rely upon extra reinforcing to minimize the stresses applied to the deck through the wheel axles. Also, in both metal and plastic applications, many height-adjust systems require a large quantity of parts, are difficult to adjust without tools, and use non-standard components. Usually it is necessary for the operator to use both hands to adjust the positions of the wheels relative to the deck. Also, a problem inherent in systems which adjust one wheel at a time is the difficulty in ensuring that all four wheels ultimately are in the same position relative to the deck.
Systems which adjust two or more wheels at once solve this problem, but at the cost of requiring the operator to move the considerable weight of the deck, engine or motor and bag. Various counterbalance systems have been developed to permit the operator to adjust the height mechanism without strain, found predominently in the environment of a metal lawn mower deck. Inasmuch as metal is a stronger medium than plastic, a minimum of attention was devoted to developing means for handling the stresses on the deck generated by forces directed through the four separate lever/bell crank arrangements. Additionally, conventional systems require several parts, are intricate, and are not easily assembled and are expensive. Also, the height-adjust lever which is used to move all four wheels simultaneously is typically mounted in an exposed position, such as on the lawn mower push handle itself or on the upper surface of the deck.
Conventionally, if it is desired to manufacture lawn mowers incorporating both types of height-adjust systems, it would be necessary to manufacture and maintain in stock two or more different lawn mower configurations. Accordingly, there has existed a need to provide a single platform configuration upon which all of the different types of height-adjust systems can be readily mounted both simply and inexpensively. The need has been especially great to provide a single configuration of a unitary plastic lawn mower deck which is adapted to support such systems, and there has existed a corresponding need for height-adjust systems that would be compatible with such a deck.